I don't really have an answer for you, but maybe the installer is 32bit? I think gtk is only needed for the installer GUI. Do you have libgtk 32b also? Or is that a unified 32/64b library? Your problem may have something to do with how the distro handles aliasing 32b and 64b libraries. Check your paths and LIB environment variables and google for 32b gtk packages for your distro, and 32b/64b library issues for your distro.

You might also read the readme at the beginning of the shar file (I think there's plain text there?). It might describe how to do a manual install. But you might run into more 32b library issues for Darwinia proper. I dunno if it can run on 64b linux.

You might also try changing the title of this thread. Maybe people would respond if they knew this is a 64b linux question. Seems like others in the forum run on 64b linux, even though the executable is not 64b native.